The present invention relates generally to a recording apparatus, and more particularly to a structure of a fixation unit in an electrophotographic recording apparatus, such as a laser printer, a copier, and a facsimile machine.
Recent electrophotographic recording apparatuses have been required to be power-saving for ecological purposes as well as fast and inexpensive. Therefore, the electrophotographic recording has a ready-to-print standby mode and a power-saving mode (also referred to as a sleep mode), and transfers to the power-saving mode in the downtime for power saving.
The electrophotographic recording apparatus has a fixation unit that fixes toner through heat and compression. The fixation unit typically includes a hollow cylindrical thermal fixation roller, a halogen lamp, arranged in its longitudinal direction in the hollow part of the thermal fixation roller, which heats up the fixation roller, a rubber roller that contacts and compresses the thermal fixation roller, and a drive gear, mounted around the thermal fixation roller, which rotationally drives the thermal fixation roller. The thermal fixation roller has a notch at its end, whereas the drive gear has a projection. The drive gear is mounted around the thermal fixation roller so that the projection is inserted into the notch. The fixation unit thus structured is relative inexpensive and used for many electrophotographic recording apparatuses.
After a transfer unit that is provided before the fixation unit transfers toner onto a recording paper, the recording paper is heated and compressed while passing between the thermal fixation roller and the rubber roller. As a result, the toner is fused and fixed on the recording paper. As the thermal fixation roller rotates, the recording paper advances between the fixation roller and the rubber rollers. The drive gear applies a drive force to the thermal fixation roller via the projection, and a contact part between the projection and the notch becomes a point of application.
The stress concentrates on the contact part and deforms the notch, resulting in the fatigue crack near the contact part. Accordingly, Japanese Patent Application Publication No. 10-111615 has been proposed a method of dispersing a force applied to the point of application using a layered structure for a thermal fixation roller to prevent the fatigue crack. Other prior art include, for example, Japanese Patent Application Publication No. 10-267111 and Japanese Patent Publication No. 8-10983.
The fixation unit thus has a heating halogen lamp, and consumes the largest power in the recording apparatus. Therefore, the power-saving mode saves the consumed power by turning off the halogen lamp and stopping heating. However, warm-up is needed to light a halogen lamp and heat the fixation roller up to the temperature necessary for printing, when the power-saving mode is returned to the standby mode for printing or at the time of initially power on. The long warm-up time means increased user's waiting time, lowering a user's expectation to fast operations or a customer's satisfaction.
A belt structure fixation method that embeds a ceramic heater into a film has already been known. It is also conceivable to increase an output of the halogen lamp. Although these methods contribute to the shortened warm-up time, the former requires expensive components and the latter is also expensive due to high electric power; they are not preferable in view of a demand for inexpensiveness.
In order to resolve the above problems, the instant inventor has eagerly reviewed instant heating by making the thermal fixation roller as thin as possible to lower its heat capacity. For example, an aluminum thermal fixation roller with a reduced thickness from the conventional thickness of 1.8 mm to 1.0 mm or smaller, for example, about 0.6 mm improves the warm-up time from about 80 seconds to about 20 seconds. However, the thin thermal fixation roller weakens its strength and the above problems become conspicuous. Therefore, repetitive use develops and grows the fatigue crack from the vicinity of the point of application, thereby damaging the thermal fixation roller. As a result, the thermal fixation roller should be replaced and its shorter life than originally expected requires user's economical burden.